Hi, I am a hobbyist and I am trying to look up the RI on stones, in particular a peridot. I went to the Properties of Gem Olivines chart and I am not sure what the columns represent. Is there a Key to know what row is what? I think it may be the Fancy B column but I am unsure, any help welcomed!

Look,I’m going to just come out and say it…your tools are of utmost importance.what I recommend is this.buy the Gemini 3 . It is an amazing tool ,and I have found it to save me countless hours of my time with many aspects of gem identity and I’m really advocating it’s purchase!

If by “Fancy B” you mean the Beta symbol, that represents the intermediate RI in a biaxial crystal, like a peridot, and corresponds to the Y-axis of the crystal. (Peridots are orthorhombic crystals and have three axes and three RIs). Alpha represents the lowest RI and corresponds to the X-axis, and Gamma represents the highest RI and corresponds to the Z-axis. There is more information on RIs and biaxial crystals in this article on optics.

Alpha, Beta, Gamma, Birefringence, and 2V are all explained in the optics article. The first two columns are just the content of Magnesium oxide and Iron oxide in olivines from different locations and different colors. SG is Specific Gravity.

Okay, likely will have more questions it looks like the properties of the peridot change according to locations? if I continue reading downward on the chart. I did not think that is possible! Learn new things all the time. Thank you!

Quick question: I found two different R.I.'s for Peridot … it looks like then the chart for olivines the last one is Fayalite and it goes up to 1.879. so that would be part of the “series members” the chart above for peridot R.I. mentions? That is why I am finding two different R.I.'s? (I found the 1.635 to 1.670 and then the one above that chart on the same page said 1.635 to 1.879 which I am guessing is series member of period, Fayalite? )

Thank you for the legend key and your responses. I will go read about optics.

Yes, fayalite is a series end-member of olivines. It’s the iron-dominant member. (Forsterite, the first row, is the magnesium-dominant member. The chart is organized by decreasing magnesium percentages).

The first range of RI values listed in the article (1.635 to 1.879), in the Peridot Information chart, shows the range from the lowest possible RI to the highest possible RI, but we have a note there to look at the information in the “Identifying Characteristics” section, since peridots can have a very variable range of RIs.

Like I recommend, naturally peridot will have different readings, based on the localand or origins of the specie’s,I was just thinking that you may have a beneficial use for one of my fav tools, Gemini 3

OK, see if we can filter the nonsense from the facts
It IS a Gem-n-Eye III, from Mineralabs.
The cost is $425, not €800, and they are currently, Out of Stock.
The way you’ve pushing this in various posts @Cj66 I thought you had shares in the company
I hope you never make the same mistake with Sapphire and Sapphirine, or Garnet and Granite

Thank you both, I also started to wonder if CJ was invested in the machine hahaha but he is just stoked about it! That is great! … … another question for everyone, I believe everything would have a R.I. will things that are opaque like turquoise or malachite show up on the scale?

Everything has an RI so it must be possible, I think the problem comes with cabochons, if the back is clean and polished, easy enough, but getting a RI from the dome is harder, there’s not a ‘flat’ spot you can set up on the refractometer table to get a reading.

I read about bobbing your head in a yes motion if there is a “spot” and try to get it half dark and half clear and that is the reading, not sure how that can be reliable , if I move my head like a snake charmer or bobbing lol its all over the place